1. Field of the Invention
The present invention relates to a method of manufacturing and protecting a silica-containing article used in the manufacture of an optical fiber. More particularly, the invention is a method of protecting the article against break-inducing particulates during shipment of the article between factories.
2. Description of the Related Art
An optical fiber is typically formed by drawing the optical fiber from a fiber preform heated to a high temperature. The fiber preform can be formed by a variety of processes. One such process, which is known as the outside vapor deposition process, is performed by applying silica-containing soot to an alumina bait rod to establish a core profile, consolidating the core profile to create a consolidated glass core blank, and drawing the core blank to a smaller diameter to create a glass core cane. The core cane is then deposited (overclad) with soot, which is consolidated to create the fiber preform. Other processes, such as modified vapor deposition (MCVD) or plasma-activated chemical vapor deposition (PCVD), known generally as inside vapor deposition processes, are performed by depositing silica on the inside of a solid glass tube. The solid glass tube with the deposit is then collapsed to form a glass core blank. Silica-containing soot is added to the outside of the core blank and consolidated to form a fiber preform. From the preform, optical fiber is drawn. Alternatively, the solid glass tube with the deposit can be collapsed to directly form a fiber preform. Still another process employed to make a preform for drawing optical fiber is the vapor axial deposition (VAD) process. The present invention has applicability in at least all of these various vapor deposition techniques.
As used herein, the term xe2x80x9coptical fiber preformxe2x80x9d or xe2x80x9cconsolidated preformxe2x80x9d shall refer to an article from which a fiber can be drawn without having to add more silica-containing glass. xe2x80x9cCore blankxe2x80x9d and xe2x80x9ccore canexe2x80x9d shall be used to refer to articles that include at least part of (but not necessarily all of) the properties of the optical core of the resultant fiber. A xe2x80x9ccore canexe2x80x9d has been drawn from a consolidated core blank into a smaller diameter, intermediate product. Thus, in some manufacturing operations, a core cane may be formed, after which additional core and/or clad glass material may be added to the core cane to form a consolidated preform.
During drawing of an optical fiber from an optical fiber preform, the optical fiber often will break. The reduction of breaks during drawing of optical fiber is a clear goal in the industry, especially since customers now request lengths of optical fiber greater than fifty kilometers.
Fiber breaks are believed to be caused at least in part by inorganic foreign particulates (e.g., ZrO2) that deposit on glass surfaces of the various articles, such as the fiber preform, core blank, core cane, and/or glass tube, produced as intermediates in the process of formation of the end-product optical fiber. These glass surfaces are reactive and can form irreversible bonds with the inorganic particulates. As shown schematically in FIG. 2, inorganic particulates 20 bond with active sites, such as OH groups, on a glass surface 10 and become part of the glass surface 10. Therefore, the particulates cannot be readily removed during standard cleaning before fiber draw. These particulates cause structural failure during fiber draw. For example, inorganic particulates on the glass surface of the fiber preform, core blank, core cane, or the glass tube, are believed to be a main cause of external fiber breaks, which occur during the draw process. Inorganic particulates on the glass surfaces of the core blank, core cane, and glass tube are believed to sometimes cause fiber internal breaks.
The inorganic particulates are present in the environment of the manufacturing plant. In addition to merely falling unaided onto the glass surfaces of the intermediate products, the particulates may be attracted to the glass surfaces by static charge. Ironically, a static charge often develops due to efforts to clean the glass surfaces.
Particulates can be removed from the glass surfaces of the intermediate products by using hydrofluoric acid as a cleaning agent. Hydrofluoric acid, however, changes the dimensions of the intermediate product because it etches the glass surface. Hydrofluoric acid is also expensive to use because it is toxic. Thus, hydrofluoric-acid cleaning is not a desirable technique for reducing fiber breaks.
It might be possible to reduce fiber breaks by manufacturing in a clean room so that there are almost no particulates to deposit on the glass surfaces of the intermediate products. This, however, would not be cost efficient.
As embodied and broadly described herein, the invention comprises a method of protecting a silica-containing article used in the manufacture of an optical fiber during shipment between factories thereby inhibiting breaks during drawing of an optical fiber. The method includes the steps of forming a silica-containing article used in the manufacture of an optical fiber at a first factory, applying a protective layer to the silica-containing article, and shipping the coated article to a second factory for further processing. The silica-containing article may be, for example, a core blank, a core cane, a fiber preform, a glass tube formed by an inside vapor deposition process, a sleeve tube used to build up a glass exterior over a core glass or rod, or any other silica-containing article used as an intermediate article in the production of optical fiber. Preferably, the silica-containing article is a glass (as opposed to unconsolidated silica soot) when the protective layer is applied.
According to one embodiment of the invention, the consolidated article has a protective layer applied thereto followed by the shipment of the intermediate article to another factory for further processing. It is an advantage of the invention that any particular intermediate, i.e., a core blank, core cane, consolidated preform, etc. may be shipped to another factory because of either a shortage in capacity or the inability to manufacture that intermediate at that particular factory. Thus, according to one embodiment of the present invention, core cane may be manufactured at a first factory, a protective layer applied, shipped to a second factory, further processed into a consolidated preform and then drawn into an optical fiber. According to another embodiment, the article may be stored at room temperature, in inventory, until production needs dictate.
In another embodiment of the invention, the consolidated preform may be manufactured at a first factory, a protective layer applied, transported to a second factory and then drawn into optical fiber at the second factory. Preferably, the preform article is cleaned prior to draw to remove any particulate(s) that may be adhered to the coating. The present invention advantageously allows certain factories to specialize in production of certain articles, e.g. core blanks, core cane, consolidated preforms or combinations thereof with subsequent application of the protective layer and subsequent shipment to the next factory. This may lead to enhanced economies and/or quality. Moreover, the present invention allows for cold transfers of consolidated preforms between factories yet with break rates comparable to, or even better than hot transfers (e.g., where the temperature of article is maintained at greater than about 600xc2x0 C.).
In a preferred embodiment, the thickness of the protective layer applied, upon curing or drying, is less than 10 xcexcm, more preferably less than 5 xcexcm, and most preferably less than 1 xcexcm. The layer is preferably an ultra-thin and non-peelable layer, which may be readily washed or cleaned. In one preferred embodiment, after being washed, the layer is preferably ablated prior to, or during, further processing. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.